SummaryIt is shown, by using depth profiling with a secondary neutral mass spectrometer and structure investigations by XRD and TEM, that at low temperatures, at which the bulk diffusion is frozen, a complete homogenization can take place in the Cu/Au thin film system, which leads to formation of intermetallic phases. Different compounds can be formed depending on the initial thickness ratio. The process starts with grain boundary interdiffusion, which is followed by a formation of reaction layers at the grain boundaries that leads to the motion of the newly formed interfaces perpendicular to the grain boundary plane. Finally, the homogenization finishes when all the pure components have been consumed. The process is asymmetric: It is faster in the Au layer. In Au(25nm)/Cu(50nm) samples the final state is the ordered AuCu3 phase. Decrease of the film thicknesses, as expected, results in the acceleration of the process. It is also illustrated that changing the thickness ratio either a mixture of Cu-rich AuCu and AuCu3 phases (in Au(25nm)/Cu(25nm) sample), or a mixture of disordered Cu- as well as Au-rich solid solutions (in Au(25nm)/Cu(12nm) sample) can be produced. By using a simple model the interface velocity in both the Cu and Au layers were estimated from the linear increase of the average composition and its value is about two orders of magnitude larger in Au (ca. 10−11 m/s) than in Cu (ca. 10−13 m/s).
Low-temperature diffusion of Fe in Pt/ 56 Fe/ 57 Fe thin films (grown on MgO (100) substrate) was investigated between 703 K and 813 K using secondary neutral mass spectrometry. The activation energy of the effective interdiffusion coefficients, evaluated by the -centre-gradient‖ method, is 1.53±0.25 eV reflecting a strong contribution from grain boundaries. This is also supported by the observed deep penetrations of Pt into the 56 Fe layer, from which the grain boundary diffusion coefficients for Pt in Fe were also estimated and 1.45±0.25 eV activation energy was obtained. A simple model, including the effect of grain boundaries to the overall intermixing at the original sharp interfaces in nanocrystalline films, is developed. This predicts that at short annealing times the grain boundary diffusion dominates, and bulk diffusion coefficients can be determined only in long time limit. At intermediate annealing times, when the grain boundaries are saturated but the bulk diffusion is still negligible, there are no changes in the composition profiles.This yields good qualitative agreement with the experimental data and offers explanation for the time and temperature dependence of the interdiffusion coefficients obtained in similar systems.
Interdiffusion processes in the polycrystalline Au (30 nm)/Cu (40 nm) thin films during annealing at 100-200C for 15 and 30 min in a vacuum with different residual-atmosphere pressures of 10 2 and 10 6 Pa and in an environment of hydrogen at a pressure of 510 2 Pa are investigated. Secondary neutral mass spectrometry complemented with transmission electron microscopy, X-ray diffraction, and atomic force microscopy is used. The intermixing of two layers is observed at the temperatures, at which the bulk diffusion can be safely ruled out. Within the Au layer, the detected Cu profiles and their time evolution are typical C-kinetic regime grain boundary profiles. Due to the much higher grain boundary diffusivity, the saturation of Au grain boundaries at the Au-rich side is hit in a very short time. The high Cu concentration level in the Au-side could be interpreted by supposing existing boundaries, which are moving and leaving behind themselves the areas with high Cu concentration close to the stoichiometric compositions. Phase formation takes place in and around grain boundaries due to diffusing component transport along moving grain boundaries.Досліджено процеси взаємної дифузії в тонких полікристалічних плівках Au (30 нм)/Cu (40 нм) під час відпалу за температур у 100-200С впро-довж 15 і 30 хв. у вакуумі при різних тисках залишкової атмосфери у 10 2 і 10 6 Па та в середовищі водню при значенні тиску у 510 2 Па. Застосовано методу мас-спектрометрії вторинних нейтральних частинок, доповнену трансмісійною електронною мікроскопією, Рентґеновою дифракцією й атомно-силовою мікроскопією. Перемішування двох шарів спостерігало-ся при температурах, за яких повністю виключається дифузія за об'ємним механізмом. Одержані для шару Au профілі Cu та їх еволюція з часом були типовими профілями C-кінетичного режиму зерномежової Па. Использован метод масс-спектрометрии вторичных нейтральных ча-стиц, дополненный трансмиссионной электронной микроскопией, рент-геновской дифракцией и атомно-силовой микроскопией. Перемешивание двух слоёв наблюдалось при температурах, при которых объёмная диф-фузия полностью исключается. Измеряемые для слоя Au профили Cu и их развитие с течением времени были типичными профилями зерногранич-ной диффузии с кинетикой C-типа. Из-за гораздо более высокой зерногра-ничной диффузионной подвижности в обогащённом слое Au насыщение границ зёрен золота достигается за очень короткое время. Высокий уро-вень концентрации Cu в слое Au можно объяснить, предполагая наличие подвижных границ, которые оставляют позади себя области с высокой концентрацией Cu, близкой к стехиометрическому составу. Фазообразо-вание происходит внутри и вокруг границ зёрен посредством перемеще-ния диффундирующего компонента вдоль движущихся границ зёрен.
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